Shaft seal with elastic sealing lip

ABSTRACT

The invention relates to a seal of the type V-ring. The seal comprises a body ( 7 ) with an inner side ( 13 ) for abutting, for example, a rotary shaft ( 1 ). The seal further comprises a lip ( 8 ) with a rear side ( 10 ) and a front side ( 9 ) with a lower portion ( 1/9  and an upper portion, the sealing surface ( 16 ). The sealing surface is intented to abut a surface rotary in relation to the seal ( 5 ), against which surface it is intended to seal. In order to prevent the seal ( 5 ) from being broken down by aggressive medium, it is made of PTFE. A resilient ring element ( 12 ) is provided to act on the lip ( 8 ) with a force, which results in that the sealing surface ( 16 ) will move in the direction to the surface it is intended to seal against. The resilient ring element ( 12 ) further is arranged so that it cannot come into contact with the aggressive medium.

[0001] This invention relates to a sealing of the type V-ring.

[0002] A V-ring can be used for sealing at a cylindric rotary body. Thiscylindric body can be, for example, a shaft for a roll in a dewateringmeans for dewatering material suspensions. Such a dewatering means cancomprise two co-acting cylindric rotary rolls, at least one of which isliquid permeable. The rolls form between themselves a nip, through whichthe material suspension is intended to pass while simultaneously beingdewatered. The material suspension usually passes through the nip upwardfrom below.

[0003] The material suspension can be, for example, a pulp suspension,and the dewatering means then can be a washing press or a dewateringpress.

[0004] Hereinafter a dewatering means according to known art will bedescribed where both rolls are liquid permeable. The rolls are formedwith liquid permeable shell surfaces, which consist of a perforatedmetal sheet attached on a roll body.

[0005] The rolls are rotary on two parallel shafts. The materialsuspension is supplied to the means so that by the rotation of the rollsit is moved upward from below through the nip whereat compression anddewatering of the material to the desired dry matter content takesplace.

[0006] After the nip the material is picked-up from the rolls by meansof a doctor blade device. The material is then transported away from thedewatering means.

[0007] The liquid (filtrate) passing through the shell surface isconducted away via channels inside the shell surface to the ends of therolls and further away from the dewatering means.

[0008] The roll arrangement, of course, can also be formed so, that thematerial suspension by the rotation of the rolls is moved through thenip downward from above.

[0009] Means of the type referred to above are described, for example,in SE 501 710 and WO 98/54401.

[0010] Each shaft is mounted in bearings, and the bearing is located ina bearing housing, which is filled with oil. In order to seal at theshaft between the oil-filled space of the bearing housing and the spaceholding the filtrate, a seal of the type V-ring of rubber is located insuch a manner, that it rotates with the shaft and has a lip restingagainst the wall of the bearing housing.

[0011] It is very important that no filtrate can penetrate into thebearing, which would be subject to great damage and in the worst casebreaks down.

[0012] At such means there is the problem that the V-ring is destroyedand requires frequent exhange. This causes very expensive shutdowns.

[0013] The present invention provides a seal with considerably longerservice life than seals of the type V-ring according to known art.

[0014] The service life of the rubber is shortened both by hightemperature and low pH. The combination of low pH and high temperatureis highly destructive. In a dewatering means of the kind described thefiltrate has low pH and high temperature. In the extreme case thetemperature can be abut 90° C. and the pH about 2.

[0015] The seal according to the invention is of the type V-ring andformed of PTFE, which advantageously is reinforced, for example withcarbon. PTFE withstands the acid envionment, but is not as elastic asrubber. In order to render the seal elastic a spring is located on theseal in such a manner, that the spring does not get into contact withthe filtrate, because it should not be exposed to the agressiveenvironment of the filtrate.

[0016] Besides, fibers in the filtrate easily adhere to the spring andcan thereby deteriorate its functioning.

[0017] The spring is arranged so that it affects the lip of the seal tobe pressed against the surface, against which it is intended to seal, inthis case the wall of the bearing housing.

[0018] The characterizing features of the invention are apparent fromthe attached claims.

[0019] A preferred embodiment is described in the following, withreference to the accompanying drawing, in which

[0020]FIG. 1 shows partly a shaft portion in a dewatering means, and

[0021]FIG. 2 shows the seal.

[0022] The dewatering means as such will not be described in detail,because it is known a.o. through the specifications referred to above.

[0023]FIG. 1 shows part of a shaft portion in a dewatering means of thekind described above. Only the upper half of a shaft 1 is shown, becausethe means is substantially symmetric.

[0024] In a bearing housing 2 on the shaft 1 a bearing 3 is located. Thebearing housing 2 is located in a hole in a wall 20, which separates amedium space 6 from the outside of the dewatering means, i.e. theatmosphere 21.

[0025] The medium space 6 contains the filtrate, which by means of thedewatering means was pressed out of a pulp suspension. The filtratecontains also a certain amount of fibers, which at the dewateringfollowed along with the filtrate.

[0026] The bearing housing, together with the shaft, encases a bearingspace 18, in which the bearing 3 is located. The bearing space 18suitably is filled with oil, but can also, for example, be filled withfat or air. A radial seal 19 seals between the bearing space 18 andatmosphere 21. The bearing housing 2 has against the medium space 6 forthe filtrate a bearing housing wall 4, against which a seal 5 of thetype V-ring acts in order to seal between the bearing space 18 andmedium space 6.

[0027] The V-ring 5 in FIG. 2 comprises a body 7 with an inner side 13,which abuts the shaft 1. The V-ring is arranged to rotate with the shaft1 at the rotation thereof. In the Figure also an O-ring 14 is located ina recess 15 in the body 7 at the inner side 13 thereof, in such amanner, that the O-ring 14 in mounted state of the V-ring 5 on the shaft1 is encased by the body 7 and shaft 1. It is the function of the O-ringto ensure that neither oil nor filtrate can pass between the V-ring 5and shaft 1. Instead of the O-ring also other types of seals can beused, for example a sealing liquid. The decision which type of seal issuitable in this position, depends on the medium used, and in certaincases no seal is needed at all.

[0028] The V-ring 5 comprises a lip 8 with a rear side 10 and a frontside 9, where the front side 9 is divided into an upper portion, thesealing surface 16, and a lower portion 17. The sealing surface 16 actsagainst the bearing housing wall 4. On the lower portion 17 a holdingmeans 11 is located, which in this case is a shelf. On the shelf 11 aresilient ring element 12 is located, which in this case is aring-shaped helical spring. Also other resilient elements can, ofcourse, be used, for example an O-ring.

[0029] The spring 12 is arranged on the shelf 11 in such a way, that itacts with a pulling force on the lip 8 and thereby pulls the lip 8against the bearing housing wall 4, so that its sealing surface 16 canabut the bearing housing wall 4.

[0030] (PTFE is not elastic, but the material “floats” in the directionof the acting force. The result, however, will be at the final end thesame as in the case of an elastic material, but with a certain delaycompared with an elastic material).

[0031] At the rotation of the shaft 1 the V-ring 5 follows along in therotation, and the sealing surface 16 of the lip abuts (seals against)the non-rotating bearing housing wall 4. At the V-ring 5 the flow willthen be such that the oil tends to flow past between the lip and bearinghousing wall. 4. Thus, no filtrate can get into the bearing housing 2and contact the spring 12 or bearing 3.

[0032] The resilient ring element 12 can also be arranged in a differentway, but so that it affects the lip 8 with a force, which results inthat the sealing surface 16 will move in the direction to the surface itis intended to seal against, which means that it is pressed against thebearing housing wall 4.

[0033] The spring 12 must not come, either, into contact with thefiltrate in the medium space 6, but shall be concealed, seen from rearside 10 of the lip 8.

[0034] The spring 12, thus, can also be located entirely enclosed in thelip 8.

[0035] It is, of course, possible to arrange advantageously more seals,suitably radial seals, between the bearing and the space containing thefiltrate.

[0036] The V-ring can, of course, advantageously also be used in othermeans where it shall seal against an aggressive enviroment, and withstill greater advantage in cases when it shall seal against anaggressive medium, where the medium in addition contains particles, suchas fibers.

[0037] The device where the V-ring shall be used can, for example, alsobe formed so that the shaft, on which the V-ring is located, is intendedto be non-rotating, and the surface, against which the lip is intendedto act, is rotary.

[0038] The invention, of course, is not restricted to the embodimentshown, but can be varied within the scope of the claims with referenceto description and Figures.

1. A seal intended to seal between a medium in a medium space (6) andintended to be arranged on a shaft (1) where the seal comprises a body(7) with an inner side (13) for abutting the shaft (1), and a lip (8)comprising a rear side (10) which is intended to be facing the mediumspace (6) and a front side (9) with a lower portion (17) and an upperportion (16) forming a sealing surface where the sealing surface (16) isintended to abut a surface (4) rotary in relation to the seal (5),against which it shall seal, characterized in that the seal (5) is madeof PTFE, and that a resilient ring element (12) is provided to act onthe lip (8) with a force, which results in that the sealing surface (16)will move in the direction to the rotary surface (4) and where theresilient ring element (12) is located so that it is concealed, seenfrom the rear side (10) of the lip (8) and by that not can come intocontact with the medium in the medium space (6).
 2. A seal as defined inclaim 1, characterized in that the seal (5) on the lower portion (17) ofthe front side of the lip has a holding means (11), on which theresilient ring element (12) is located.
 3. A seal as defined in any oneof the preceding claims, characterized in that the resilient ringelement (12) is a ring-shaped helical spring.